PCBs

Polychlorinated biphenyls (PCBs) are a class of organic compounds
(specifically organochlorides) with 2 to 10 chlorine atoms attached to
biphenyl, which is a molecule composed of two benzene rings. PCBs were widely
used as dielectric and coolant fluids, for example in transformers, capacitors,
and electric motors. Due to PCBs' toxicity and classification as a persistent
organic pollutant, PCB production was banned by the United States Congress in
1979 and by the Stockholm Convention on Persistent Organic Pollutants in 2001.
Concerns about the toxicity of PCBs are largely based on compounds within this
group that share a structural similarity and toxic mode of action with dioxin.
Toxic effects such as endocrine disruption and neurotoxicity are also
associated with other compounds within the group.